Pressure Evolution and Gas Accumulation of the Fourth Member of the Shahejie Formation in Dongying Depression, Bohai Bay Basin

Key words: 
• Dongying depression /
• cracking gas /
• dynamic hydrocarbon accumulation /
• paleopressure /
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Abstract: After the paleopressure buildup by means of measured pressure, mudstone sonic log interval and fluid inclusions, the pressure evolution model of the fourth member of the Shahejie Formation is analyzed in Minfeng area, Dongying depression. The results show that, different periods of reservoir formation correspond to different pressure system in Es4 reservoir, Minfeng area: the hydrocarbon accumulation of Sha 2last stage of Dongying was accomplished in a higher pressure system; the hydrocarbon accumulation environment of the last stage of Ng was normal pressure; and after the middle and late period of Nm the cracking gas in the central area of sub sag was formed in a high pressure system. The dynamic evolution process of formation pressure is the results of integrated effect of multiple factors, the first high pressure was due to uncompaction of the highrate deposition of the formation, and the hydrocarbongeneration made a little contribution; a large amount of hydrocarbon played an important part in the form of the second high pressure, in addition,  the sedimentation acted as the auxiliary role. Under the influence of the decrease of geothermal gradient, fracture, sand bodypressure discharge and the deepburial of gas reservoir, the gas reservoir founded in Sha 4 reservoir, Minfeng area is mainly normal pressure.